The spinal column is a highly complex system of bones and connective tissues that provide support for the body and protect the delicate spinal cord and nerves. The spinal column includes a series of vertebral bodies stack atop one another, each vertebral body including an inner or central portion of relatively weak cancellous bone and an outer portion of relatively strong cortical bone. Situated between each vertebral body is an intervertebral disc that cushions and dampens compressive forces exerted upon the spinal column. A vertebral canal containing the spinal cord is located behind the vertebral bodies. The spine has a natural curvature (i.e., lordosis in the lumbar and cervical regions and kyphosis in the thoracic region) such that the end plates of the upper and lower vertebrae are enclosed toward one another.
There are many types of spinal column disorders, including scoliosis (abnormal lateral curvature of the spine), excess kyphosis (abnormal forward curvature of the spine), excess lordosis (abnormal backward curvature of the spine), spondylolisthesis (forward displacement of one vertebra over another), and other disorders caused by abnormalities, disease, or trauma (such as ruptured or slipped discs, generative disc disease, fractured vertebrae, and the like).
Patients that suffer from such conditions often experience extreme and debilitating pain, as well as diminished nerve function. Posterior fixation for spinal fusions, decompression, deformity, and other reconstructions are performed to treat these patients. The aim of posterior fixation in lumbar, thoracic, and cervical procedures is to stabilize the spinal segments, correct multi-axis alignment, and aid in optimizing the long-term health of the spinal cord and nerves.
Spinal deformity is the result of structural change to the normal alignment of the spine and is usually due to at least one unstable motion segment. The definition and scope of spinal deformity, as well as treatment options, continues to evolve. Surgical objections for spinal deformity correction include curvature correction, prevention of further deformity, improvement or preservation of neurological function, and the restoration of sagittal and coronal balance. Sagittal plane alignment and parameters in cases of adult spinal deformity (ASD) are becoming increasingly recognized as correlative to health related quality of life score (HRQOL). In literature, there are significant correlations between HRQOL scores and radiographic parameters such as Sagittal Vertical Axis (SVA), Pelvic Tilt (PT) and mismatch between pelvic incidence and lumbar lordosis.
Spinal disorders, such as degenerative processes of the human spine, loss of disc height and lumbar kyphosis, result in a reduced HRQQL. The skeleton compensates for changes in the spine caused by these disorders to maintain balance and horizontal gaze of the subject. However, such compensation requires effort and energy from the subject and is correlated to a lower HRQQL score. Current surgical planning tools do not evaluate or include compensatory changes in a subject, leading to an undercorrection of a deformity in a patient that undergoes the surgical plan and procedure. Therefore, a need continues to exist for systems and methods that include compensatory changes as part of surgical planning.